Inhomogeneity of fluorescence lifetime and intensity in a plasmonic nanocavity

Abstract

The plasmonic nanocavity featured with strongly increased local density of photonic states (LDOS) in the nanoscale hotspots, is capable of significantly modifying the radiation properties of the coupled emitters, which has led to abundant applications such as plasmon laser and single photon sources. Thus, there is a strong motivation to understand the radiation dynamics of emitters within nanocavities. However, the radiative properties are highly dependent on the local electromagnetic environment, which varies at the nanoscale inside the cavity. Experimentally achieving a high spatial resolution of the radiative properties of fluorophores in the fixed size plasmonic nanocavity has been elusive to date, especially to verify the spatial dependent luminescence lifetime variations and intensity of fluorescent molecules within a well-defined plasmonic nanocavity. Herein, a convenient and universal plasmonic nanocavity with dimensions of about 9 nm is fabricated by using the particle-film coupling model. By tuning the longitudinal position of fluorescent molecules in a plasmonic cavity, a similar trend was observed in fluorescence lifetime and intensity, in which increasing first and then decreasing as the molecules positioned from the bottom mirror to top particles, and the longitudinal resolution is as low as 2 nm. The experimental results and theoretical calculations provide a basis for understanding fluorescent materials and nanocavity interactions, building a bridge to fabricate of nanoluminescent devices and bioluminescent materials.